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In the sympathetic division, neurons are mostly adrenergic (that is, epinephrine and norepinephrine function as the primary neurotransmitters). Notable exceptions to this rule include the sympathetic innervation of sweat glands and arrectores pilorum muscles where the neurotransmitter at both pre and post ganglionic synapses is acetylcholine .
Sympathetic nervous system stimulation causes vasoconstriction of most blood vessels, including many of those in the skin, the digestive tract, and the kidneys. This occurs due to the activation of alpha-1 adrenergic receptors by norepinephrine released by post-ganglionic sympathetic neurons.
A preganglionic fibre may synapse to 15–20 postganglionic fibres. The postganglionic neurons extend across most of the body. [4] Upon exiting the sympathetic chain, the fibres enter a less-myelinated gray ramus communicans. There is still a myelin sheath present – but in far lower amounts compared to the white ramus communicans.
Each spinal nerve receives a branch called a gray ramus communicans (pl.: rami communicantes) from the adjacent paravertebral ganglion of the sympathetic trunk.The gray rami communicantes contain postganglionic nerve fibers of the sympathetic nervous system and are composed of largely unmyelinated neurons.
The SCG receives pre-ganglionic sympathetic afferents from the ciliospinal center which synapse in the ganglion. Post-ganglionic efferents then leave the SCG and join the internal carotid nerve plexus of the internal carotid artery, accompanying first this artery and subsequently its branches to reach the orbit and ultimately innervate the dilator pupillae muscle to mediate pupillary dilatation.
It has also been shown that modifications in the cholinergic input at the celiac ganglion also led, via the superior ovarian nerve, to modifications in ovarian steroidogenesis. [1] [2] [3] Most of the fibers of the superior ovarian nerve come from the postganglionic sympathetic neurons of the celiac ganglion.
The internal carotid plexus is a nerve plexus situated upon the lateral side of the internal carotid artery. It is composed of post-ganglionic sympathetic fibres which have synapsed at (i.e. have their nerve cell bodies at) the superior cervical ganglion. The plexus gives rise to the deep petrosal nerve. [1]
In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there are both sympathetic and parasympathetic ganglia which contain the cell bodies of postganglionic sympathetic and parasympathetic neurons respectively.